Field of the Invention
The present invention relates to a lens to be provided on a light emitting element lamp, etc. that uses a light emitting element such as an LED.
Description of the Related Art
More specifically, the present invention relates to a lens having a specific surface shape for light-distribution control to achieve desired light distribution when the lens is used, the desired light distribution means an elongated and smoothly-diffused light distribution having long and short axes, of the light from a light emitting element which, without said lens, illuminates a surface to be illuminated in a substantially isotropic and rotationally-symmetric manner, and to a light emitting device using such lens as well as a method of manufacturing thereof.
A lamp, in which a light emitting element, typically an LED, mounted on a base board is combined with a lens that enables desired light distribution state of the light from the light-emitting element, has been known. Lenses used in these lamps, for example when used as a backlight of display devices or the like, are required to have desired light distribution characteristics of a backlight, and when used as a street light, they are required to have light distribution characteristics of the street light suitable for road surface.
In the prior art, as a lens for light emitting elements which provides light distribution characteristic having long and short two axes, for example, the lenses disclosed in Patent Documents 1 and 2 have been known.
The lens of Patent Document 1 is a lens that “provides a light emitting diode which can improve the luminance distribution of conventional light-emitting diodes in which brightness rapidly decreases as the opening angle from the optical axis increases” (paragraph No. 0010), and that “achieves the above objectives by applying a modification to the surface shape of sealing members” (paragraph No. 0011), and that is characterized by the following: “in the light emitting diode comprising a chip placed on a predetermined optical axis and a transparent sealing member for sealing the chip from the front side of said optical axis, a curved surface portion is formed on the front surface of the sealing member, and a cross-sectional shape of this curved surface portion along a first plane including the optical axis, is composed of a waveform curved surface having a concave curve near the optical axis and convex curves at both lateral sides of the concave curve, and, a cross-sectional shape of this curved surface portion along a second plane that is parallel to the optical axis and is perpendicular to the first plane is composed of a convex curve” (paragraph No. 0012).
The lens of Patent Document 2 is “an optical device for providing desired shape to the light beam” (paragraph No. 0001), which “relates to an illuminated surface, in particular, an illuminated surface having a longer length relative to its width, such as road, street or highway” (paragraph No. 0001), and is “an optical device for providing an elongated shape for the light beam” (paragraph No. 0010), wherein “a diopter is an optical surface that separates the two light propagation media having different refractive indices” (paragraph No. 0018), and the optical device “has two mutually-perpendicular symmetry planes IIA and IIB that are also perpendicular to a base plane to which the base plane 5 is inscribed, as shown in FIGS. 2A and 2B. The planes IIA and IIB intersect at the center line 22 of the lens 2” (paragraph No. 0031), and, “in order to provide an elongated shape for the light beam, it is necessary to expand the light beam. Therefore, the exit diopter 4 has a first converging portion 41, a second converging portion 42, and a diverging portion 43 that bridges the first and second convergent portions 41 and 42” (paragraph No. 0032). And the lens has a surface shape wherein “when the curve included between positions C and D is rotated about the axis 23, the entire exit diopter 4 is obtained” (paragraph No. 0034).
In these conventional light-distribution adjustment lenses, an elongated light distribution pattern is obtained as follows: in order to make an oval-like pattern having a longitudinal direction instead of circular pattern, the lens does not have a simple spherical surface, but have the cross sectional shape, cut along the longitudinal direction of the illuminance pattern, in which two peaks are present with recessed center between them, so that the light passing through the center of the cross section is diffused on both sides, and the lights are converged into the two directions inclined from the lens center line. Such bimodal shaped lens is referred to as “bat wing lens” from its unique shape of light distribution.
FIGS. 10A, 10B(1), and 10B(2) illustrate an oblique perspective figure of such conventional light distribution adjustment lens, and FIGS. 11A and 11B shows its illuminance pattern and a light distribution characteristic. Since FIG. 11A is a black and white drawing, the illuminance pattern in the left plan view is explained; the inner area of the bright ring represents a portion of high intensity shown in the right intensity scale, and the outer area of the ring in the left plan view represents a portion of low intensity. In all of the illumination intensity distribution diagrams in the present application, illumination intensity is higher in inner area of the bright ring than in outer area. Regarding the light distribution in the longitudinal direction, the light is distributed more in directions inclined from the direction of the lens central optical axis 4 passing through the lens center than in the direction of the axis, so that the light illumination range is elongated; however, its illuminance pattern is, as shown in FIG. 11A, a pattern of the light distribution of a thin oval shape with pointed tips. It was not possible to obtain an illuminated surface with a light distribution wherein a larger area is illuminated while ensuring a constant width in a smoothly-diffused light distribution in the short-axis direction, and a smoothly-diffused light distribution is also obtained in the long-axis direction in an oval-shaped distribution with not-pointed tips, but having certain area. In addition, it was also impossible to obtain a complex light distribution as required, while maintaining an oval shaped smoothly-diffused light distribution, or while maintaining a certain area of light distribution.
That is, in these conventional lenses for light emitting elements, while the light distribution becomes an elongated oval shape due to the long axis cross-sectional shape of the lens of the light emitting side in the longitudinal direction, the lens shape of the light emitting side of the short-axis cross section perpendicular to the longitudinal direction is composed of convex curves (paragraph No. 0012 in Patent Document 1) or is circular or a cross-sectional shape of quadratic curved surface (paragraph Nos. 0033, 0034 in Patent Document 2), and therefore, in the light distribution near the short-axis direction, enhanced effects of rotationally symmetrical and isotropic lens shape for the light source of the light emitting element are reflected on an illuminated surface; as a result, the light distribution in the short-axis direction including the light axis is intensified, and the light does not extend from around the short axis to the longitudinal direction, so that sufficiently homogeneous illuminated-surface is not obtained. In addition, in the illuminance pattern, since the light distribution at the short axis including the optical axis is strong, the overall elliptical shape tends to be an ellipse close to a diamond shape.